The present invention relates to an electric rolling steel door, and more specifically to a motor drive for an electric rolling steel door.
FIGS. from 6 through 9 show a conventional motor drive for an electric rolling steel door. The motor drive comprises a speed reducer 2', a motor 1', and a control box 4'. The speed reducer 2' comprises a power input shaft 26' coupled to the motor shaft 11' of the motor 1' by belt wheels 112' and a transmission belt 111'. The power input shaft 26' is mounted with a first chain wheel 22', a bearing 243', and a third chain wheel 24' on the bearing 243'. The third chain wheel 24' comprises a big sprocket 241' and a small sprocket 242'. A bearing 233' is mounted on the power output shaft 21' to support a second chain wheel 23', which comprises a big sprocket 231' and a small sprocket 232'. A fourth chain wheel 25' is mounted on the power output shaft 21'. Chains 27' are coupled between the first chain wheel 22', the second chain wheel 23', the third chain wheel 24' and the fourth chain wheel 25'. The power output shaft 21' is mounted with a sprocket 211', which is coupled to a sprocket 51' at a shaft 52' of the rolling steel door 5' by a chain 212'. A sprocket wheel 28' is slidably mounted on the power input shaft 26' and retained in place by a spring 283'. The sprocket wheel 28' comprises two pins 282'. A lever 3' is operated to press a push rod 31' thereof against the sprocket wheel 28', causing the sprocket wheel 28' to be moved to a locating pin 261', for enabling the sprocket wheel 28' to be turned with a chain 281' upon pulling of the chain 281' by hand. Therefore, when power fails, the chain 281' can be pulled by hand to take up/let off the rolling steel door 5'. This structure of motor drive is still not satisfactory in function. The drawbacks of this structure of motor drive are outlined hereinafter.
1. Because a high power motor is needed to turn the low performance speed reducer, much power energy is consumed during the operation of the motor.
2. The complicated and heavy structure of the motor drive is expensive to manufacture, and requires much installation space.
3. Because low performance of the speed reducer, additional torsional spring means must be installed to automatically take up the shaft of the rolling steel door.
4. Because no brake means is provided, the rolling steel door cannot positively stopped at the desired position.